In an airplane, the time between when I realize that things are not as they should be and the time when I won't be thinking anymore could be measured in minutes. That is a pretty chilling thought for me...
Don't worry! Most of the time, you never know what hit you in an airplane catastrophe. If the aircraft breaks up at 35,000 feet (as a result of a mid-air collision, fuel tank explosion, terrorist attack, etc.), you're none the wiser. You'll probably be killed by flying debris within a second, and if you survive the break-up, you'll have the oxygen boil out of your blood a few seconds after that.
Much more frequently, you'll hit a mountain while flying in zero visibility. Zero seconds to worry.
A large portion of accidents occur when the plane lands. Tail or wing strike, skidding off the runway, etc. These calamities are likely to occur even more rapidly than a car crash. You probably won't be able to complete the sentence "Oh shi----!"
Or maybe your plane is overweight and can't get enough power to take-off properly. In this case, you've got 20 seconds max to contemplate your fate. And it will probably take you 10 seconds realize that it is really happening. "Why is it taking so long to take off? Is the plane really flipping upside down? Is this REALLY happening?? Oh, oh, yes, it is..."
Being in a plane that plummets to the ground for a minute or two isn't that likely. When seated on your flight, you should really be aware that your life could be snuffed out without warning at any minute.